1. Field of the Invention
The present invention relates to a frequency modulation device for irregularly modulating an operational frequency and a switching mode power supply (SMPS) using the frequency modulation device.
2. Description of the Related Art
A switching mode power supply (SMPS) is a device that rectifies an input AC voltage to an input DC voltage (DC-Link voltage) and that converts the input DC voltage to an output DC voltage having a different level. The output DC voltage can be higher or lower than the input DC voltage. The SMPS is generally used for electronic devices such as a battery charger of a mobile phone or an adapter of a laptop computer.
In some SMPS switching noise is generated when a switching operation is performed. The switching noise can cause electro-magnetic interference (EMI) between electronic devices which receive power through the SMPS. The switching noise is generated by harmonics of a switching operation frequency of a switch of the SMPS. The EMI can cause problems by disturbing an operation of peripheral electronic devices. Accordingly, sometime additional devices such as a filter are provided to the SMPS to prevent the EMI. However, this increases the production cost.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.